Crystal field energy levels of Eu3+ and Yb3+ in the C2 and S6 sites of the cubic C-type R2 O3

In the cubic C-type rare-earth (R) sesquioxides, C-R2 O3, the trivalent R ions (R3+) occupy two different crystallographic sites with S6 and C2 symmetries. The R ions in the C2 lattice site have been studied intensively whereas the properties of the R3+ ions in the S6 site are largely unknown or the data are contradictory. Based on the spectroscopic data reinterpreted by a phenomenological crystal field (cf) analysis a new interpretation was obtained for the energy level scheme of the Eu3+ ions in the S6 site of C-R2 O3. The cf parameters obtained were then used to predict the energy level scheme of the Yb3+ ion in the same host lattices. In the prediction, the evolution of the cf parameters along the R series studied earlier in the R oxide and garnet systems was used. The relationship between the cf strength parameter and the overall splitting of the 2S+1 L J levels as well as the relationship between the barycentres of the free ion levels were used, also, to reinterpret the energy level scheme of the Yb3+ ion in the C2 site of C-Y2 O3